Don't tell bind software version

Backport from !500 (merged)

Was changed in a MR later from "DNS managed by ISPConfig" to "DNS-Server", but imo it should be "unknown"

install/tpl/named.conf.options.master

@@ -21,6 +21,8 @@ options {
 	dnssec-enable yes;
 	dnssec-validation yes;
 	dnssec-lookaside auto;
+
+	version "unknown";
 	
 	allow-transfer {none;};